Recent wastewater regulations promulgated by the U.S. Environmental Protection Agency (EPA) require secondary treatment as the minimum acceptable level of treatment prior to discharge of surface waters. Increases in industrial wastes discharged into domestic sewage treating plants has also increased significantly the need for improved wastewater treatment methods to remove hazardous chemicals and to meet the secondary treatment standards.
In many parts of the country, the available supply of fresh groundwater has become contaminated with toxic chemicals or the groundwater table has been drastically lowered by effects of inadequate rainfall. In these areas, advanced wastewater treatment and reuse of wastewater will become a necessity in the foreseeable future.
Seidel has proposed, in U.S. Pat. No. 3,770,623 herein incorporated by reference, a system for purifying waters polluted with oily pollutants, coarse suspended materials, slime, colloidal material, dissolved inorganic compounds and/or pathogenic organisms by a three-stage process, in the first stage of which gravitational separation of floatable oily pollutants and heavy sediment is accomplished, in the second stage of which the remaining aqueous material is treated in filtration beds containing plants having nodes to remove slime and colloidal material by filtration and in the third stage of which the effluent from the second stage is passed into a bed containing plants which can use the dissolved impurities as nutrients. For waters heavily contaminated with pathogens, plants with bacterial nodules will be used in the second or third stages.
Serfling et al. have proposed, in U.S. Pat. No. 4,169,050, to treat wastewaters using pollution-consuming, floating aquatic plants which have high surface area, submerged, activated bio-web substrates of high fixed bacterial film area and activity.
Carothers has proposed (U.S. Pat. No. 3,728,254) a process for recycling waste products, which utilizes conventional activated sludge aeration tanks and a "trickling filter effect" to enhance aeration and bacterial growth in the aeration tank.
Wolverton, "New Hybrid Wastewater Treatment Systems Using Anaerobic Microorganisms and Reeds," presented at a Seminar on Innovative Wastewater Treatment Technology, Louisville, Ky. (Apr. 23, 1981), incorporated herein by reference, has reviewed the art with respect to the separate uses of anaerobic microorganisms and vascular aquatic plants for the treatment of wastewaters and has proposed an improved treatment system combining the foregoing to treat wastewaters after a preparatory anaerobic settling step.
It will be apparent that higher standards required for recycle or discharge of wastewaters require the development of improved wastewater treatment technology. Present economic conditions in the United States make highly desirable the development of technology which consumes less energy and is more cost effective and more efficient than wastewater treatment methods presently available.
It is the object of this invention to provide a simple and effective method for purifying wastewaters, which method is low in energy requirements and economical in operation.